Dave

ShowMe Winelands

Cape Dams Levels – weekly report nr. 003

as at 12th November 2018

[Wemmershoek Dam, 90.2% full. Photo: DWS]

The levels of the six main SW Cape dams, as reported by DWS for the week, showed a smaller net outflow of 6.1 M.cuM and total volume of water stored fell to 648.8 M.cuM; i.e. from 73.6% to 72.9% of overall capacity.

During the same week in 2017 the total volume stored fell by 8.7 M.cuM (0.9%)

A week ago the Metro was still drawing heavily from the Steenbras dams but that that has reportedly changed and water is currently also being drawn from Voelvlei Dam. The Berg River and Theewaterskloof dams should now start to reflect the effect of outflows to agriculture.

The following chart shows the weekly change in the total amount of water stored. Note that I have changed the colour coding in order to make it easier to follow present changes [2017/18 is now shown in green and current 2018/9 is now shown in red, emerging left].

[click on the graph to see an enlarged version]

I expect that the red line will tend to follow the general shape of the green and black lines for the coming three months, probably lying somewhat between the two and more towards the black line (which denotes 2016) due to the latest easing of restrictions. In both instances supplies of water to the irrigation boards had commenced by this stage. It is likely that around end of January 2019 that they will diverge more sharply as distribution of water to agriculture continues in 2019, whereas it was cut off during February 2017, as the green graph clearly shows.

It is expected that agreement on water allocations will be reached and announced by DWS this coming week. There will be no gazetting needed as an emergency condition no longer applies.

Once DWS has set water allocations for the irrigation boards and municipalities, the latter will then decide and announce appropriate levels of restriction to be applied to their communities in order to conform with the allocations, and publish the changed tariffs.

The weather is quickly taking on the normal summer pattern with the dominant high pressure zone statically positioned over the Cape. No significant rain is forecast until next week when light rain will brush the southernmost Cape, perhaps bringing small inflows to the Steenbras dams. Beyond that there is some promise of thundery weather around 5th/6th December that may see 20-30mm of rain falling if one finds oneself under the storm.

El Nino is continuing to move into place but is not fully there yet – it needs two more months of above-average sea temperatures to become classified as a fully-fledged El Nino condition.

The Cape Metro has just released this revised drought monitoring chart which clearly shows the “safe zone” extent to which stored water could be drawn down across the summer season. This too shows that under the worst circumstances the low point of storage of some 300 M.cuM could be reached at around May 2019. This would be a comfortable situation with adequate reserves.

Against this background, a number of readers have expressed concern about the possible ill-effects should current restrictions be eased.

While this is a natural response after the stresses of the past few years, I feel that I must reiterate that we do have considerable stores of water and it needs to be used. An appropriate outcome is that water should be used steadily across summer so that by following winter there is space for fresh rainfall to recharge the dams back up to a good level (ideally 80% or better), as has often happened before. This will still leave a good reserve in case the following rains are less strong. The fall-back would be to reimpose restrictions if the following rains fail altogether.

Because if we do not use the water, then tariffs will be forced to remain too high and cause unnecessary hardship. Furthermore, good following rains would cause the then over-full dams to spill and that new water would flow to the sea and be completely wasted.

So we should use but certainly not abuse our water. However, maintaining maximum restrictions is not the correct answer. This past drought is likely to be the worst that will happen in our lifetimes. It would be irrational to impose an unnecessarily harsh lifestyle based on an exceptional event that is unlikely to recur.

To remain fully informed you may like to check the following items weekly

Tom Brown.Retired international businessman with a background in Finance and IT; and now a fruit farmer, with a passion for the weather and climate.Views expressed in this article, and comments in response, are those of the writer and commenters alone and do not necessarily reflect the views and opinions of ShowMe, nor is any warranty hereby given as to suitability for any purpose of a reviewed enterprise or as to the quality of offered advice, products, services or value. Copyright ShowMe Paarl. All rights reserved. Copy only with prior permission.

The latest data point on the cumulative storage for Cape Town dams shows that inflows are now tracking the median value for the last 70 years. If the rains pick up even more, we could start beating the average, which is vital if we want make up the shortfall created by the last few years. If it falls back, then it is even more critical that we maintain a conservative approach to water usage well into next winter.

Over 200,000 Cape Town households use less than 6000 litres/month

(Repeated from Cape Town City media release) 29th May 2018

The monthly update of the water map for April shows that 211 000 households have achieved the dark green water-saving dot for their water saving efforts. This marks a slight decrease but it is heartening to see that a large number of households are still going green.

The dark green dot for water saving is awarded to households who are using 6 000 litres or less per month.

Grey dot with small dark green centre: estimated water meter reading of less than 6 000 litres per month

Grey dot with small light green centre: estimated water meter reading of less than 10 500 litres per month

Solid grey dot: excluded property (including: sectional title property or group housing / undeveloped property / water use is zero / no available information for the property / estimated water meter reading of more than 10 500 litres per month)

Please note: The map simply indicates water consumption for free-standing houses, not compliance with water restriction limits. Households with higher consumption may have many people living on the property, or may have an undetected water leak.

The map shows consumption information from meters read in the previous month, and may include a portion of consumption from the preceding month. This information is updated from the third week of the following month.

Households using more than 10 500 litres per month are not shown on the map. Remember that consumption higher than 10 500 litres per month (no green dot) does not necessarily indicate water abuse.

We appear to be following the 1 in 5 year or lower 20th percentile when it comes to water storage in Cape Town supply dams. To be anywhere near being “out of the woods” for the next few years, the red dots would have to be following the dark blue, or even light blue line. We’re not even above the green line! Best we all realise the water shortage is far from over and at this point, it looks like we’ll be living the “new normal” for some years to come.

Take advantage of the rain tank specials when the likes of Builders Warehouse starts trying to offload the stock they got in at the tail end of the panic buying.

Calculating the date for ‘Day Zero’ at any moment in time is tricky; it involves a number of factors which can vary from day to day. This results in the date ‘jumping’ about from week to week and can be confusing and disconcerting. We asked permission from DWS to publish the weekly graphs that they use to monitor the system drawdown, which may help a little to manage members’ fears and expectations.

This graph uses red dots to plot the ACTUAL water in the 6 major dams supply the CoCT (Theewatersdkloof, Voelvlei, Berg River Dam, Wemmershoek and the two Steenbras Dams) against PROJECTED levels that are the result of modelling the system. The projected storage assuming low inflows like last year are shown using the dark black dashed line and represent the MINIMUM TARGET. it is important that the storage RED DOTS remain above the BLACK DASHED LINE. That means we avoid dropping the levels of the dams below 13.5%, which gives us a narrow safety margin of about 5% before the water in the dams becomes unusable.

Keep RED above BLACK and we’re on TRACK…

If you look closely at the red dots you will see that around the 29th January they were beginning to diverge below the minimum target. However, subsequently due to the reduction in the combined agricultural and urban demands and the donation of some water by the Groenland Water User Association from Eikenhof Dam the red dots are starting to converge back towards and even beyond the target. This is in essence why “Day Zero” was shifted out into July.

It is conceivable that a wetter winter will be experienced than last year and the various coloured lines represent the probability of these scenarios. For instance, there is about a 50% chance that the storage will follow the green line and reach 700 million m3 providing the planned demand savings are achieved. Similally, there is a 10% chance of the dams filling and less than 2% chance that similar inflows to last year will be experienced.

The system was modelled taking the following variables into account:
a) Rainfall
b) Evaporation
c) Urban potable usage from the dams supplying CoCT
d) Agricultural usage from the dams supplying CoCT

It did NOT account for:
a) Augmentation from CoCT boreholes and desalination plants
b) Augmentation from Eikenhof dam
c) The slightly unseasonal rainfall and inflows received in November and December 2017

The BLACK DASHED line is the projected storage assuming low inflows like last year.

The RED Dots are the actual weekly storage of the system.

“Dead storage” is the water in the dams that cannot be accessed due to pumping limitations. Berms and temporary pumps are being installed to reduce the dead storage.

The reason that Misverstand dam is excluded is because it is a relatively small dam with only about 10 million m3 storage (of which about 80% was unavailable due to pumping limitations) which serves the West Coast and some irrigation.

The totals include the following dams: Theewaterskloof, Voëlvlei, Berg River, Wemmershoek, Upper and Lower Steenbras.

For those who need a bit of info on stochastic modelling:

The probabilistic trajectories were derived using stochastic modelling. “Stochastic” means being or having a random variable. A stochastic model is a tool for estimating probability distributions of potential outcomes by allowing for random variation in one or more inputs over time. The random variation is usually based on fluctuations observed in historical data for a selected period using standard time-series techniques. Distributions of potential outcomes are derived from a large number of simulations (stochastic projections) which reflect the random variation in the input(s).

Its application initially started in physics, although it is now being applied in engineering, life sciences, social sciences, and finance.

The stochastic streamflow generator used in the system model was developed by well known University of KZN Professor Emeritus, Geoff Pegram.
{http://civeng.ukzn.ac.za/Schoolleadershipandstaff/GeoffreyPegram.aspx

As beautiful as it is, the Western Cape is a water-scarce part of the world (much like other successful tourist regions like Southern California and Western Australia) and is vulnerable to the effects of climate change and susceptible to periodic droughts. At present the Western Cape is experiencing a significant drought. Traditionally we experience most of our rain during the winter period, starting May and continuing to August. However, rain can be experienced anytime of the year.

Cape Town and the Western Cape are open for business in spite of the current drought. Visitors and delegates will arrive in a place with a significant breadth and depth of experiences, and exceptional beauty, but we encourage you to be mindful of water-wise tourism and business travel when you’re here.

To counter the short-term effects of the drought, the City of Cape Town has put in place a number of initiatives to increase the supply of water and make provision for extreme water shortages. There are still many places across the Western Cape that are not as severely affected by the drought, such as the nearby Garden Route and the Cape Overberg.

Dams – Latest levels: Winelands and Cape Town

Report nr. 89 (updated 12th February 2018) on the main dams serving

Cape Town City and nearby Boland/Overberg towns

Last week, net outflows from the main dams dropped further to 5.8 M.cuM, or 0.7% of total dam capacity; vs the preceding week’s higher 7.2 M.cuM. Combined dam levels dropped during last week from 25.2% of capacity to 24.5% of capacity

In 2017, the main dams dropped by a far larger 10.4 M.cuM, falling 1.2% to 35.7% of full capacity.

Current status?

Combined water stored in the 6 main dams fell to 218.1 M.cuM (133 M.cuM of easily accessible water) (last year, levels dropped to 317 and 235 M.cuM respectively over the same period).

How long will the remaining fresh water last?

It is now clear that DWS has cut the use of water for irrigation purposes at or about the agreed 40% level. At the same time, the non-agricultural use of water has also dropped sharply as the new level-6b restrictions come into effect. According to my calculations, this past week the use of 5.8 M.cuM of water from the dams could probably have been split more or less as follows:

metro 3.6 M.cuM,

evaporation 1.7 M.cuM

other municipalities 0.4 M.cuM

residual agriculture 0.3 M.cuM

assume some rainfall run-off -0.2 M.cuM

Therefore the main target remains to drive use in the Metro down to the target of 450 ML/day and together with the other smaller municipalities down to a combined result less than 500ML/day.

The main irreducible current cause of the weekly drop in the combined dam levels is evaporation. Fortunately, evaporation will begin to decline as the ambient temperatures start to fall. By April it will be less than half of what it is now, and by June it will have halved again.

Of course a major once-off positive contributor over the coming 6-8 weeks will be water transferred from the Groenland Water Users Association pumped across into Steenbras Dam. This is expected to amount to some 8-10 M.cuM of fresh water, which should add two week’s supply to the WCWSS for the Metro and other municipalities. A life-saving, selfless donation by those farmers.

This unexpected inflow of water taken together with continued reduction in water use by residents indicates that water currently stored in the dams could well last until between mid- and end-June before the implementation of stage-2 (collection/rationing) of water supplies may be required.

The chart below indicates the position at the start of February. It is too early for a mid-month correction but the early indications are that my currently predicted water consumption for the month will again prove to be too high and that in February we will use less water than the 37.8 M.cuM expected. Remember also that the red block indicates that point where, had our water usage followed the same pattern as last year, we would already have hit “Day Zero”.

What actually is going on?

1) As this CoCT graph shows, most agricultural use of water has been closed off by DWS and the earlier steep rising usage curve is now starting to “flat-line” at/about the set maximum of 58 M.cuM for the total water used. Other than remaining pockets of unused quotas, use of water from the main dams by agriculture is all closed for this season.

2) It may be seen from the photo at the head of this report that DWS is modifying Voelvlei and Theewaterskloof dams to enable part of the water that lies in the deepest part of the dams to be pumped up to the level of the abstraction points, so that more of the water can be made available for the Metro and municipalities. At TWK (shown) the work involves creating a temporary berm to hold flows from the Sonderend River at a higher level for easier abstraction. Should these natural flows be insufficient, then more water will be pumped up from below this temporary berm to above it so that water can be sent through to the Berg River side. Through these modifications, DWS expects to be able to draw both these dams down to about 6% of capacity should that become necessary.

3) Residents of the Metro and other smaller municipalities are obviously making great strides to reduce their consumption of fresh water. As a result, Cape Town City which until recently seemed so stuck at a usage of 600ML/day has over a few weeks dropped sharply to ave 493ML/d during this past week. This is an outstanding result and shows just how well the residents are reacting to the call to use less water. The goal is to as soon as possible get this daily consumption down to 450ML/d or less. And it seems to me that could be achieved before end-February. We done everyone.

The following heavily altered CoCT tracker chart shows in overall terms what is going on (see here for a detailed explanation of how the chart is to be read).

City of Cape Town held its prediction of “Day Zero” at 11th May 2018 (point red ‘X’ in the chart). Although CoCT remains conservative in its estimates, this may be adjusted soon to a yet later date.

We are today at point red ‘Y’ (24.5% of capacity on 12th February). However, we are not only benefiting from the savings made by agriculture (the blue striped zone “E”, but more importantly as anticipated residential water usage reductions kick in (the blue-shaded zone “H”) we are starting to follow the curving dotted white line, trending toward point “I” on the revised lower line “C” at which the authorities would have to implement stage-2 collection/rationing of the disaster plan.

Our hope then is that winter rains together with early water production from augmentation initiatives (area “K”) will lift us on to the red dotted line “L” denoting steady recharge of the dam storage.

Therefore, I would like to suggest that instead of the dark negativity of “Day Zero” we now set ourselves a positive fixed target that we call “Success Day” and make that target getting to 30th June with at least 100 M.cuM of water left in the main dams. This would represent about 11% of capacity and, assuming that the DWS is indeed prepared to drop the dam levels down to 6-7%, would leave a safety margin of some 4-5%; so that even if we receive no rain at all there would still be enough water in the dams to support a stage-2 rationing program through until end-2018 by which time a number of augmentation initiatives will be producing extra water to relieve the situation.

In support of this notion of “Success Day” the present augmentation plans comprehend the production of 80ML/day of fresh water by July and 180ML/day of fresh water by December 2018.

More positively, if we can reach end of June with that much water still available, then we will be well into the rainy season and even with weak winter rainfall, recharge of the dams would have begun.

What are the authorities doing now?

The City of Cape Town reports that 526 ML/day of water was consumed from all sources but that it only used 493 ML/day drawn from the main dams. This implies that the augmentation initiatives have progressed to the point that they are producing the difference i.e. 33ML/d of fresh water.

The Metro has embarked on a massive information campaign using all possible ways to make the broader population aware of the problem and encouraging them to save water.

The Metro is also developing a program of volunteers to assist with the many tasks that will have to be dealt with if water supply to the taps is cut off, such as assisting at water collection points and caring for the most vulnerable. Read more here to see how you might apply to help.

The level-6b restrictions and sharply increased tariffs appear to be having a marked effect in encouraging less use of water. This is supported by further roll-out of pressure reduction systems to reduce losses through piping and system failures.

CoCT has announced that it intends to release details of the Points of Distribution on Sunday 18th February. Sensibly, work on these expensive installations will be delayed until the last possible moment, in the hope that they are not needed at all.

The two initial temporary desalination plants at Monwabisi and Strandfontein are reported to be about 70% complete and should start producing fresh water next month. On the other hand, work on the V&A desalination plant has been delayed by intervention of the DWS Minister wanting a desalination unit from Durban to be installed there.

Drilling into the Cape Flats and TMG aquifers is proceeding.

DWS is making rapid progress on constructing the berm and pumping installations at Voelvlei and Theewaterskloof dams. It should be noted the cost of this work, being R12-15 million in each case, has been funded by DWS.

Cooperative Government and Traditional Affairs Minister Des van Rooyen stated that central government is working on the possible proclamation of a national state of emergency. To date three provinces (Western, Eastern and Northern Cape) have been declared local disaster zones, but this planned escalation would mobilise more resources of the state to assist all parts of the country facing the widening shortage of water.

2) Check out water usage for your property and of neighbours, friends, using this interactive map.

What ought you to be doing?

1) Be “water warriors” at home and at the place of work. Make extra efforts to cut down on all possible use of water. By using a basin and large sponge, reduce the water used to shower to under one litre. One can do this daily with hair washed and oneself totally cleaned. All one gives up is the luxury of standing under a hot shower; a small price to pay for water security.

2) Join dependable social media groups and form local WhatsApp groups so as to stay in touch and benefit from tips and suggestions on how to reduce use of water. Have a look at this link.

3) Take care of personal hygiene and reduce health risks. Treat grey water being saved for flushing with Jik or vinegar to prevent smells and possible spread of bacteria. Wash hands regularly.

If you are a business owner or manager, I strongly recommend that, if you have not already done so, meet with your employees and take them into your confidence regarding what you believe may happen to your business as this situation unfolds. The situation is unprecedented and no one will have points of reference or past experience to draw upon. Employees are likely to be concerned and perhaps even fearful about their jobs, incomes and how they will cope.

By discussing the matter you would simultaneously make them all fully aware of the seriousness while encouraging their participation in implementing ways to cut down on water usage and may even generate good ideas on how to mitigate the possible negative impact of water rationing. One concept to consider – if it would be appropriate in the event of a possible slow-down or loss of some business – is to perhaps adopt a policy of work-sharing where those working in the same departments or doing the same work could between them share whatever reduced work might still be available in return for flex-time time off while earning proportionately reduced incomes. The main advantage being that some familiar work is far better than none.

Will the weather help?

Well, as predicted, that cold front came through last weekend and variable amounts of rain fell across the SW Cape. Gratifyingly some rain fell in all the dam catchments. Run-off will already have reached dams with more to come. A good 33 mm of rain was measured at Dwarsberg which feeds the Berg River and TWK dams.

As I write there is a low pressure system north of Cape Town feeding rain with the possibility of thundershowers from the North West down towards Agulhas. Rains could be fairly widespread as this chart from NOAA/CPC indicates, with the possibility of stronger rainfall behind the mountains in the catchments area of the large dams. If you are lucky enough to be under a cloud …

Here is the rainfall chart for the dam catchments for the period since 1st April 2017. This tracks rainfall that is measured actually falling at the dams.

Retired international businessman with a background in Finance and IT; and now a fruit farmer.

Views expressed in this article, and comments in response, are those of the writer and commenters alone and do not necessarily reflect the views and opinions of ShowMe, nor is any warranty hereby given as to suitability for any purpose of a reviewed enterprise or as to the quality of offered advice, products, services or value. Copyright ShowMe Paarl. All rights reserved. Copy only with prior permission.

OK, so we’re all at some point in the journey to “50 litres per person per day”. None of us want to be queueing for 25l at a Point of Distribution. In the 1st post, we covered the need to find and read your water meter and know where the main stopcock is. In the 2nd we discussed the fact that the toilet in your house swallows more potable water than anything else, after any pool or garden you may have. Today, we talk about baths & showers.

Step 3. The shower.

Baths are so 2014; no one should be bathing much any more. You will battle to make the 50l per person target, if you are bathing instead of showering. If you have access to alternate sources of water (like a wellpoint, or rainwater) your bath can be used to store that water to be used for flushing the loo and cleaning the house. If you have a small child that needs to bath, you can either invest in a baby-dam, or buy a large basin.

Buy a low flow shower-head for your showers, or at least fit flow restrictors behind the showerhead. Shower every other day or every 3rd day if you can, using a washcloth and basin or a spray-bottle to sponge-bath on the days you don’t shower. You’re not going to die, and in fact you may find your skin will in fact be healthier for it. If you need to, use a bit more deodorant than you’re used to. Obviously if you work in a coal-mine every day, you’re going to have to be creative about bathing – maybe save some of the grey water to get the worst off!

Stand in a large basin while you shower, catch the cold water in a bucket while waiting for the hot to come through (and throw that in the bath) or better still, while summer is still baking the dry land, skip the hot and wash with cold. Wet yourself as quickly as you can, turn off the tap, soap and lather, then only turn the tap back on to rinse the soap off. This should not take more than 120 seconds and can be achieved in closer to 60 once you get practiced and if your hair is not as long as Rapunzel.

The grey water you catch in the basin you stood in can be transferred to one of a number of buckets you need to organise next your loo so that you no longer have to flush with clean potable water.

Another source of grey water is the washing machine, but more on that in the next post…